The present invention relates to a brushless motor and, particularly, to a structure of a brushless motor which is suitable to drive a rotary drum of a video tape recorder.
Generally, a conventional brushless motor includes a driving portion for producing rotational torque to be used to drive a utilization, a frequency generator portion for producing an electric signal indicative of a rotational speed thereof and a pulse generator portion for producing an electric signal indicative of a position of a rotor thereof. Each of these portions of the brushless motor may be constituted with a permanent magnet and a coil, etc. A typical example of such brushless motor is disclosed in, for example, Japanese Patent Application Laid-open No. S63-93770.
In order to simplify a structure of such conventional brushless motor and hence to reduce a manufacturing cost thereof, various systems have been proposed. In one system such as disclosed in Japanese Utility Model Application Laid-open No. H1-180871, a single magnet is commonly used for both a driving portion and a frequency generator portion, so that the number of magnets is reduced by one. In another system, a connecting pattern of a driving coil of a driving portion and a connecting pattern of a coil of a frequency generator portion are arranged in a common plane. Therefore, a space economy is improved to some extent. In a further system such as disclosed in Japanese Utility Model Application Laid-open No. S62-185475, a single magnet is used commonly for both a frequency generator portion and a pulse generator portion, resulting in elimination of one magnet.
Unfortunately, however, it is still impossible to use a single magnet for generating driving torque, a frequency signal and a pulse signal, simultaneously.